JPS63170851A - Cadmium electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To improve the utilization factor of a negative electrode and the quick charge characteristic by processing a cadmium electrode with an activator liquid, then reducing it once, next forming a porous layer of nickel by electrolytic plating. CONSTITUTION:A cadmium electrode, particularly the cadmium electrode obtained from cadmium oxide mainly by the paste method, is first processed by an activator liquid. Next, a reducing process is applied, then a porous layer of nickel is formed by electrolytic plating. Accordingly, the utilization factor of a negative electrode and the effect on the quick charge characteristic can be stably maintained for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in cadmium electrodes for alkaline storage batteries.

BACKGROUND OF THE INVENTION As is well known, storage batteries used as various power sources include lead-acid batteries and alkaline batteries. A typical alkaline battery system is a nickel-cadmium storage battery.

The development of a sintered electrode for this nickel-cadmium storage battery has made it possible to significantly improve charge/discharge characteristics, lifespan, low-temperature characteristics, etc., and the adoption of a sealed type has improved handling.

However, although efforts are being made to improve energy density and reduce costs, they are not sufficient. For example, in order to improve energy density, foamed electrodes have been developed for nickel electrodes, but it cannot be said that sufficient cost reductions have been achieved. On the other hand, with regard to cadmium electrodes, the development and commercialization of a paste method instead of a sintering method has made it possible to reduce costs to some extent, but the current situation is that the utilization rate of cadmium has not been sufficiently improved.

In order to improve the utilization rate of such cadmium electrodes and to improve custom fast charging, it has been proposed to form a conductive and porous layer on the surface of the cadmium active material. When it comes to forming a porous layer on the surface of these containers, a carbon or metal layer is most commonly used. Cadmium active materials include metal cadmium, cadmium oxide, cadmium hydroxide, and other cadmium compounds, but in consideration of economic efficiency and filling requirements for the electrode, a material composition mainly composed of cadmium oxide is most preferable.

Problems to be Solved by the Invention It has been revealed that forming a conductive and porous layer on the surface of the cadmium active material is highly effective in improving the utilization rate and rapid charging of cadmium electrodes for alkaline batteries. We have shown that cadmium oxide is a promising material for cadmium active materials, and that it is preferable to form a carbon layer or a copper or nickel layer as a metal layer by electroless plating. Ta.

Among these, it is clear that simply forming a carbon layer by coating a layer of fine graphite powder and a binder has a significant effect on improving oxygen gas absorption ability during rapid charging. It has become. However, the carbon layer is subject to repeated normal charging and discharging, severe overcharging and discharging, long-term storage,
Under harsh conditions such as use at high temperatures, carbon may oxidize or fall off, causing the initial excellent effects to be lost.

On the other hand, although nickel is the most superior material in this respect, in the case of a paste-type electrode mainly made of cadmium oxide, it does not form a good layer no matter whether it is electroless or electrolytically plated. For example, in the case of electroless plating, the process is sensitizer → activator → electroless plating, but unlike copper plating, when cadmium oxide is used as the main material, a uniform plating layer cannot be formed under normal plating conditions. I can't get it. If a large amount of sensitizers and actuators are used, plating can be done to some extent, but this does not avoid contamination with impurities and increases costs. The same is true for electrolytic plating, as it is impossible to directly plate on cadmium oxide1, and it is difficult to perform actepator treatment.

Means for Solving the Problems According to the present invention, the cadmium electrode is first subjected to an activator treatment, then the cadmium electrode is phosphoreduced, and then nickel is electrolytically plated. Although high-temperature treatment in hydrogen is another method of reduction, in order to avoid changing the composition of the cadmium electrode as much as possible, reduction with hydrazine or formaldehyde in a dilute alkali at room temperature is preferable.

As described above, in electrolytic plating, an activator treatment is performed in the same way as in electroless plating, and furthermore, in electroless plating, the plating process is directly started, but in this application, -
Electrolytic plating is performed after the phosphorus reduction process. It was found that this method enables porous nickel plating with unprecedented uniformity.

In this way, first, a cadmium electrode, especially a cadmium electrode obtained by a paste method using mainly cadmium oxide, is first treated with a commercially available activator solution, then a reduction step is added, and then a layer is formed by electrolytic plating of nickel. , the effect on the utilization rate of the negative electrode and the rapid charging characteristics can be maintained stably over a long period of time.

EXAMPLE A paste-type cadmium electrode using cadmium oxide t↓, which is the most effective of the present invention, will be explained in detail as an example.

First, a paste is prepared by adding commercially available cadmium oxide to a 3-part ethylene glycol solution of polyvinyl alcohol, a 6-part polyethylene fine powder by weight, and vinyl chloride-acrylonitrile short fibers at a 0.6% weight ratio. A nickel-plated bunching plate made of iron with a thickness of 0.161NIII, a pore diameter of 1.51ff, and a porosity of 50% is coated on both sides of the plate as a core material, smoothed through a slit, and the thickness is 0.
．． Adjust to 6. The paste was dried at 20° C. for 2 hours to obtain a paste-type cadmium electrode.

Next, a commercially available activator solution for electroless nickel plating is diluted six times with water, and the cadmium electrode is impregnated with this. After drying at 80°C for 20 minutes, it is immersed for 5 minutes at 20°C in a solution containing 15% (volume) commercially available formalin in an aqueous caustic potash solution with a specific gravity of 1.10. Through this treatment, the cadmium pole changes to a pale black color as it changes to black, which is a noble metal mainly made of palladium.

Next, electrolytic nickel plating was performed using a known nickel Watt bath at a current density of 46° C., somA/Cm, and a time of 3 minutes. It was air dried and then dried at 8o'C for 1.5 hours. The weight increase due to plating was approximately 2 g/d.

As an example of a battery, a AA sealed nickel-cadmium storage battery was used. Therefore, the cadmium electrode obtained in this way was cut into 39ffll width and 261mm length.
The lead plates were attached to two predetermined locations by spot welding. This was partially charged in advance for 9 minutes under the conditions of a current of 1 ohm and an aqueous caustic potash solution with a specific gravity of 1.16, washed with water, and dried. As a counterpart electrode, a known high capacity sintered nickel electrode was selected, also having a width of 39 m and a length of 220 m. In this case as well, lead plates were attached at two locations.

A polyamide nonwoven fabric was used as the separator, and lithium hydroxide was dissolved at 26 da/l in a caustic potassium aqueous solution with a specific gravity of 1.18 as the electrolyte. Let's call this battery Mu. The nominal capacity ii is 2.45 Ah.

Next, for comparison, a battery using a cadmium electrode obtained by adding an electrolytic plating process immediately after the actepator treatment was added as B, and a battery fO using a cadmium electrode that was not treated at all was added.

First, when we investigated the utilization rate of the cadmium electrode itself used in these batteries A-C, we found that 0, I C, 16 at 25°C for charging.
Terminal voltage O, S V of nickel-cadmium test battery with cadmium pole rule, 0.30 at 26°C for the same time and discharge.
The conditions were set up to. As a result, the battery's cadmium electrode has a superior utilization rate compared to others, with a power consumption of 387 mAh/y.
showed that. 363 mAh/I, Ci
d 359 mAh/y.

Next, the rapid charging characteristics of batteries A to C were investigated.

The maximum internal pressure of each battery was investigated by performing 1C charging at -3°C. As a result, battery B (4o, ekg/d, battery B
2.3 kg/cyA, 3.1 to 9 for battery C
/d. Also, the maximum pressure when charging at 1.50℃ at -3℃ is trxl-1kti/ct.
l.

3. With battery B. takq/c East Battery C 6-8k (
It was 1/ctA.

Thus, it can be seen that the cadmium electrode of the present invention not only slightly improves the utilization rate but also significantly improves the rapid charging characteristics of the battery used. On the other hand, if plating is simply performed after the activator treatment, it is thought that the plating will proceed near the core material of the cadmium electrode, so the effect will be better than untreated, but it will not be as good as the present invention.

Effects of the invention By first applying activator treatment to cadmium electrodes, especially paste-type cadmium electrodes that are mainly made of cadmium oxide, and then applying nickel electrolytic plating after adding a reduction process, it becomes possible to significantly improve rapid charging. .

Claims (2)

[Claims] (1) A cadmium electrode for an alkaline storage battery characterized by adding a reduction step after activator treatment and then forming a porous layer of nickel by electrolytic plating. (2) The cadmium electrode is of a paste type using cadmium oxide as a starting material, and the reduction after activator treatment is
The cadmium electrode for an alkaline storage battery according to claim 1, prepared by using a reducing agent such as formaldehyde or hydrazine in caustic alkali.